Den 10-03-2015, skrev Ron D.:
Many microwave issues including the one you describe can also be the
magnetron.

I'd go through those tests first. If it lost heating capacity gradually or
sometimes would shut off too early, I would definitely suspect the magnetron.

Btw, it is relativily easy to measure the actual heating capacity of a
microwave oven.

Measure the time to heat a glass of water to boiling point.

200g water * 4.184 J/(gK) = 836.8 J/K
285g glass * 0.840 J/(gK) = 239.4 J/K
Total heat capacity: 1076.2 J/K

Temperature rise 100C-15C = 85K
Energy used = 1076.2 J/K * 85K = 91477 J
Time: 2min 24 sec = 144 sec
Power = 91477 J / 144 sec = 802.4 J/s = 802.4 Watt

This is in SI-units.

If your measurements are based on the phalanges of ancient english
royalty, your constants may differ.

--
Je suis Charlie